The people who are scanning the skies for asteroids with the potential for colliding with Earth found an object 2007VN84, which they found would approach within 12,000 km of the Earth's center. Naturally, they put out an alert.
The object in question turns out to be man-made. It's the Rosetta spacecraft, swinging by Earth en route to comet Churyumov-Gerasimenko.
Belatedly, somebody thought to check the orbital elements against the Satellite Situation Center. The Minor Planet Electronic Circular blames the mixup on the lack of a comprehensive publicly available database of man-made objects in space.
(h/t Steinn Sigurdsson)